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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

ALUMINIUM

275

faintly alkaline reaction. The liquid is boiled for some time and the alu-
minium and ferric hydroxides filtered off, washed, dried and weighed in
the ordinary manner. This amount, less that of the ferric oxide previously
found, gives the alumina and hence the aluminium.

If the iron has not been determined previously, it may be estimated
in presence of aluminium by means of cupferron.

For this purpose, 100 c.c. of the liquid in the flask are treated in a 250
c.c. beaker, with constant shaking, with 6% aqueous cupferron (ammonium
salt of nitrosophenylhydroxylamine) until the precipitation of the iron is
complete (p-i gram Fe requires 0-833 gram of the reagent). The end of the
reaction is detected by pouring a little of the reagent down the side of the
beaker; when iron is still present, a reddish-brown precipitate is formed
whereas in absence of iron a white, crystalline precipitate is formed owing
to the slight solubility of the reagent in an acid medium.

After the precipitation of the iron, the liquid is left for 15-20 minutes
and then filtered, the precipitate being thoroughly washed first with 2N
hydrochloric acid, then with slightly ammoniacal water to eliminate all
traces of the reagent, and finally with distilled water. The moist filter
and precipitate are then carefully ignited in a porcelain crucible, the weight
giving the ferric oxide.1

8. Determination of the Nitrogen.—From 3 to 4 grams of the sample
are dissolved, in a flask fitted with a tapped funnel and a gas delivery tube,
with 10% sodium hydroxide solution, the gas generated being collected in
dilute hydrochloric acid. At the end of the action, the flask is boiled for
a further 15 minutes to displace all the ammonia and the nitrogen in the
hydrochloric acid then determined colorimetrically with Nessler solution,
comparison being made with a standard ammonium chloride solution.

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* *

Aluminium of good quality should be white with only a faint blue tint and
should be highly ductile and malleable, while its fracture should be finely crys-
talline, uniform, and free from sponginess or slag. Its specific gravity should be
between 2-6 and 2-7 (the value increases with the degree of impurity) and the
percentage of aluminium at least 97-98, the total amount of elements commonly
accompanying the aluminium (silicon, iron, copper) not exceeding 1-5-2%.
According to Moissan, a particularly harmful influence on the strength and
durability of the aluminium, especially when this is to come into contact with
water, is exercised by sodium, which may be present in the proportion of o-i-
0-4% (Moissan) or, according to some, in even larger amounts (up to 4%).
According to Foundry, aluminium also contains 0-04-0-12% of nitrogen. The
compositions of various samples are given in the following table (Moissan,
Campredon, Lunge) :

1 In the liquid from which the aluminium and iron have been separated, the mag-
nesium is determined in the usual manner,cid, heated again to oxidise the